Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, December 1st, 2020 - 7:00AM
Expires
Wed, December 2nd, 2020 - 7:00AM
Forecaster
Andrew Schauer
Avalanche Warning
Issued: December 1, 2020 6:00 am
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

We have issued a BACKCOUNTRY AVALANCHE WARNING through the National Weather Service for the Turnagain Pass area and surrounding mountains.

Avalanche danger is HIGH as a strong storm system that moved into the area yesterday afternoon continues through today. Heavy snowfall, strong winds, and rain will make large natural avalanches likely, and they will be large enough to bury, injure, or kill a person. Travel in avalanche terrain is not recommended.

SUMMIT LAKE TO SEWARD REGION: The avalanche warning extends down through the Summit Lakes area down to Seward, due to heavy precipitation, warm temperatures, and strong winds.

*Roof Avalanches: Warming temperatures and rain could cause roofs to begin to shed their snow. Pay special attention to children, pets and where you park your car.

Special Announcements
  • From Alaska DOT & PF: There will be intermittent traffic delays Tuesday, December 1, 2020 on the Seward Highway and Portage Glacier Highway for Avalanche Hazard Reduction work. From mileposts 88 to 85 on the Seward Highway, South of Girdwood. Near milepost 5 and Bear Valley on the Portage Glacier Highway. Motorists should expect delays of up to 45 minutes between 10:00 AM and 3:00 PM. Updates will be posted on the 511 system. http://511.alaska.gov/
  • Want to learn more about forecasting mountain winter weather?? Join us and guest meteorologist Kyle Van Peursem tonight, Dec 1st from 7-830pm on Zoom for our first Forecaster Chat series!!
  • Avalanche Education Scholarships are available and the deadline is Today, December 1st.
    Please see the ‘Scholarships’ page for more details and get your application in!
Thanks to our sponsors!
Tue, December 1st, 2020
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
High (4)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
High (4)
Below Treeline
Below 1,000'
Avalanche risk
High (4)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

In the past 24 hours, the mountains have received 12-18” snow, equaling 1.1-1.7” snow water equivalent (SWE), and heavy precipitation is expected through the day. As of this morning, most of this precipitation has fallen as snow, but we are anticipating rain as high as 2500 feet throughout the day. Easterly winds were sustained 15-35 mph last night, with gusts as high as 110 mph. This combination of heavy snowfall and strong winds is rapidly loading start zones, and the snowpack will quickly loose strength when liquid water (read ‘rain’) is introduced. The snowpack does not react well to rapid change, and today we are making some big changes in a hurry. We can expect to see widespread natural activity during this storm, with large avalanches running far into runout zones. Avalanches failing within the new snow will be up to 4’ deep, and that doesn’t even take into account the potential for avalanches failing on weak layers deeper in the snowpack (see problem #2). At mid- to low elevations, these avalanches will involve wet snow, and they will have the potential to reach very long runout distances. There is no question about it, the current situation is dangerous, and it will get worse before it gets better. For now, we need to stay out of avalanche terrain.

Click Here for a video checking in from Seattle Ridge yesterday.

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

As if we didn’t already have enough to worry about with the storm snow issues, we also still have weak, faceted snow deep in the snowpack in many locations in our advisory area. This storm is placing a heavy burden on weak snow, and it is possible that we will see avalanches failing over 6′ deep in the snowpack. For today, we have plenty of clear signs indicating very dangerous conditions and avalanche terrain should be avoided entirely.

 

Tincan. We still don’t trust the weak snow near the ground. Photo: Eric Roberts. 11.30.2020

Weather
Tue, December 1st, 2020
Yesterday: In the past 24 hours, the mountains have received 12-18” snow, equaling 1.1-1.7” snow water equivalent (SWE), with lower totals at lower elevations. Easterly winds were sustained 15-35 mph last night, with gusts as high as 110 mph. Today: As of this morning, most of this precipitation has fallen as snow, but we are anticipating rain as high as 2500 feet throughout the day. We will receive up to 12-18” more snow by the end of the day, equaling 1.0-1.2” water. Below 2000’, almost all of this will fall as rain, with .75" rain expected in Girdwood. Winds will be 15-25 mph out of the southeast, with high temperatures in the low- to mid 30’s. Tomorrow: This storm will taper off tonight with low temperatures hovering in the low- to mid 30’s. Lingering precipitation will be mixed rain and snow, with 1-2” snow and about 0.1” water. South winds will be 5-15 mph, and high temperatures will be in the low- to mid 30’s.   PRECIPITATION 24-hour data (6am - 6am)
Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 28 17 1.7 74
Summit Lake (1400') 18 6 0.6 27
Alyeska Mid (1700') 30 13 1.15 73
RIDGETOP 24-hour data (6am - 6am)
Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 19 ENE 34 110
Seattle Ridge (2400') 24 ESE 15 43
Observations
Recent Observations for Turnagain Pass
Date Region Location
05/18/21 Turnagain Observation: Tincan Ridge
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04/27/21 Turnagain Observation: Tincan Ridge
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04/25/21 Turnagain Observation: Sunburst
04/24/21 Turnagain Observation: Airplane obs
04/24/21 Turnagain Observation: Corn biscuit
04/23/21 Turnagain Avalanche: Lynx Ck Drainage
04/23/21 Turnagain Avalanche: Sunburst
04/23/21 Turnagain Observation: Center Ridge Turnagain pass
Riding Areas
Updated Tue, June 01st, 2021

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Placer River
Closed
It is packrafting and jetboat season!
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.